Distillation apparatus

ABSTRACT

The invention relates to purification of liquids by distillation. Processes of this nature have long been known. One well known example is the conversion of sea water to fresh water by distillation. The purpose of the invention is to accomplish the distillation with maximum efficiency. As is well known, in distilling a liquid the impure liquid is heated so as to vaporize the portion of the liquid sought to be recovered, thereby separating the material to be recovered from the material to be rejected by virtue of the fact that they exist in different phases. Having separated the components by phase the vapor is then transferred to another region where its temperature is lowered so that it condenses in a region separate from the impure mixture and thus is recovered.

J. D. WIXSON DISTILLATION APPARATUS Aug@ 6, 1974 5 ShoetnShest 1Original Filed Aug. 6, 1969 Aug. 6, 1974 J. D. wlxsoN 3,837,945

DISTILLATION APPARATUS original Filed Aug. e, 1969 5 shntsnaet s /l H Hf/ U /8 To. l GEV/34.5

l-LOW CONCENTRTE IN HIGH CONCENTRATE OUT PUMP OUT

/Q /l/ f//f/ /f//f/ /71 l HIGH PUMF L* PUMP LOW CONCENTRATE l/V CONC ENTRATE CONDE NSATE OUT O U T 3 O United States Patent Otiice 3,827,945Patented Aug. 6, 1974 3,827,945 DISTILLATION APPARATUS James D. Wixson,902 Marine St., Boulder, Colo. 80302 Original application Aug. 6, 1969,Ser. No. 850,325, now Patent No. 3,637,465. Divided and this applicationJan. 24, 1972, Ser. No. 220,391

Int. Cl. B01d 3/00, 3/08, 3/28 U.S. Cl. 202-177 8 Claims ABSTRACT OF THEDISCLOSURE The invention relates to purification of liquids bydistillation. Processes of this nature have long been known. One wellknown example is the conversion of sea water to fresh water bydistillation. The purpose of the invention is to accomplish thedistillation with maximum efiiciency. As is well known, in distilling aliquid the impure liquid is heated so as to vaporize the portion of theliquid sought to be recovered, thereby separating the material to berecovered from the material to be rejected by virtue of the fact thatthey exist in different phases. Having separated the components by phasethe vapor is then transferred to another region where its temperature islowered so that it condenses in a region separate from the lmpuremixture and thus is recovered.

This is a division of application, Ser. No. 850,325 filed Aug. 6, 1969,now Pat. 3,637,465.

This invention relates to a distillation method and apparatus, moreparticularly to a method and apparatus for distilling a liquid underconditions which are near theoretically optimum heat recovery.

A typical object of such distillation process is to make potable waterfrom sea water or water otherwise contaminated with impurities. Highoperating costs have evolved in most prior art processes which have asufciently high output rate to be commercially interesting, primarilybecause of high energy consumption.

It is a primary object of this invention to provide a distillationsystem which reduces the energy necessary to produce a unit mass ofdistilled liquid to an amount which is near the theoretical minimum.

A further object of this invention is to provide a distillation systemof either large or small scale, which yields a cheap, pure condensate. l

It is another object to provide a distillation system in which heat Howsfrom the fluid being cooled to the fluid being heated in a manner whichis essentially recirculating counterow exchange. This specificallyincludes (l) counterow heat exchange between the raw liquid entering thesystem on one hand and the condensate and concentrate leaving the systemon the other; (2) recovery of heat of condensation from the condenserand reintroduction of this heat into the evaporator; (3) counterilowheat exchange from the cooling superheated gas or steam to that vaporwhich has just evaporated and is being superheated to remove entrainedimpurities.

These and other objects of the invention for obtaining the highestpossible quantity of liquid recovered from its solution per energy costat a high mass rate of flow will become more apparent upon furtherreading of the specification and claims, taken in conjunction with thefollowing illustrations, of which:

FIG. 1 is a diagrammatic illustration and ow diagram of the method andan apparatus incorporating the basic concepts of this invention.

FIG. 2 is a diagrammatic illustration representing an alternateembodiment of the apparatus of FIG. 1.

FIGS. 3 and 4 are diagrammatic illustrations of the basic principles ofthis invention according to alternative methods for accomplishing theinvention.

The apparatuses of all the figures generally include an insulatedhousing 10 in which the internal walls consist of many layers ofconcentrically arranged heat exchanger surfaces. Diagrammatically, thisis shown as spaces 12 and 14 which are in heat transfer relationshipwith each other. Interior thereto is an interconnected evaporator andc011- denser. The evaporator is generally designated by the numeral 18while the condenser is generally designated by the numeral 20. Theevaporator in the embodiment of FIG. 1 is designed to provide fordiverging flow and the condensing section 20 provides for converging owof the recirculating vapor. The latter includes a converging nozzleportion 22 and a condensation or stagnation chamber portion 24 whichsurrounds the converging nozzle portion and is in heat transferrelationship therewith. The diagram shows only one nozzle; in actualconstruction a multiplicity of converging nozzles may be surrounded bythe stagnation chamber 24. A motor 26 is adapted to drive an impeller 28for the continuous circulation of vapor between the evaporator andcondenser, as shown by the arrows. Other apparatus includes inlet 30 andpump 32 which connect with heat exchanger wall 12. Flow continuesinteriorly into conduit 34. This conduit is a part of a circuit by meansof which the raw solution at boiling temperature is recirculated throughthe evaporator, perhaps owing along its walls as shown at '40,optionally countercurrent to the vapors passing through the divergingnozzle as shown by the arrows. This liquid flow may in some instances bea falling film of boiling liquid, the unevaporated portion of whichdrops into receiving tray 42 and is recirculated. Some of this highlyconcentrated liquid is thereafter removed through conduit 44 at a ratedependent upon the desired concentration of the recirculating liquid.This concentrate leaves through pump 46. It will normally be desirableto utilize the heat of said concentrate by a heat transfer,diagrammatically shown at 48, whereby its heat is transferred to andiucreases that temperature of the incoming raw solution in zone 12.

Condensate designated by the numeral 50 is removed from the stagnationchamber 24, passing through conduit 52 and thence into the secondannular zone 14, to finally exit through pump 54.

For the purpose of illustration, if a pressure greater ythan atmosphericexists, pumps 46 and 54 are hydraulic motors to recover the work of pump32. If the evaporator pressure is less than atmospheric, then 46 and 54become pumps and 32 is a hydraulic motor.

Typical operation is described with reference to producing potable waterfrom sea water. This involved pumping the sea water from inlet 30 bypump 32 into zone 12, which is in heat transfer relationship with zone114. This zone 14 contains condensate which yields up its heat as itflows toward pump 54. Heatflow through the heat exchanger Wall, typifiedby zones 12 and 14 within the insulated housing 10, has raised thetemperature of the sea water to nearly its boiling temperature at thepoint where it enters conduit 314. Additional heat is added each time itpasses through conduit 36, located in the higher temperature stagnationzone 24, thereupon the nearly boiling liquid ows through inlet 40, therefalling countercurrent to the vapors within the diverging zone.Unevaporated concentrate collects in tray 42, a portion of it isthereafter removed from the system in a predetermined mass ratio to theentering liquid, through conduit 44 and heat exchanger 48, by means ofpump 46. In the evaporator 18 the recirculating vapor slows; itstemperature rises to slightly above the boiling temperature of therecirculating liquid 40. Thus heat is transferred from the recirculatingvapor to the recirculating liquid. This vapor together with the newlygenerated vapor passes to the widest point of the diverging chamber. Atthis point,

indicated by the numeral 27', flow is quite slow and a substantialdegree of superheat may be achieved. If desired a recirculatingcounterflow heat exchanger 56, 58, 60 may assist in such superheating,drawing heat from the steam approaching the condenser and transportingit to the steam leaving the evaporator 18. The flow then continues intothe condenser. Here a portion of the vapor is diverted into thestagnation zone 24 and yields up its heat of condensation to exchanger36 and nozzle 22, resulting in condensate or potable water 50 which isthereafter removed from the system. This condensate passes throughconduit 52 into zone 14 where it is in heat exchange with the incomingraw liquid in zone 12. The remaining portion of the vapor continues itscirculation into the converging nozzle portion 22 of the condensingchamber where its velocity increases substantially and its temperaturedecreases to somewhat below the condensation temperature of the stagnantvapor. The nozzle or nozzles represented by the numeral 22 conduit heatfrom stagnation zone 24 into this recirculating steam. Thus, the heat ofevaporation is removed from the vapor in stagnation zone 24 and thesteam in zone 2'4 condenses and collects at 50. Vapor in conduit 25, 27`is maintained in circulation by impeller 28. As it leaves the throat 25of nozzle 22 the conduit widens and the vapor slows down, increasing intemperature to somewhat above that of the recirculating liquid insection 40 of the evaporator. Thus, the heat of condensation acquired innozzle 22 is returned as heat of evaporation to evaporator 18. The vaporiiow path is to be everywhere designed for minimum flow drag. Theevaporator and the condenser are thus connected by an aerodynamicallyeflcient, continuous, closed conduit or path wherein vapor remains inconstant l'low. Temperature conditions within the system may beinitially established by means of, for example, a heating coil 70, whichalso continuously provides the additional heat necessary to replace anylosses. The provision for a small cross-sectional area in the convergingnozzle 22 of the condenser and a large crosssectional area in theevaporator 18 insures that the vapor temperature in nozzle 22 will beslightly less than condensation temperature and in the stagnation zone,and that the vapor temperature in the large cross section 27 is slightlygreater than evaporation temperature in the evaporator 18. Flow throughthe converging nozzle causes acceleration, decreased pressure andtemperature of the vapor within it, and causes absorption of heat fromchamber 24 through the conducting nozzle walls. In throat 25 the vaporis at its highest velocity and lowest temperature. The provision for astagnation zone in which the converging nozzle is surrounded with vaporpermits the heat of condensation to be conducted from the stagnant zonethrough the conduit walls of the nozzle 22 to the vapor inside thenozzle and transported therewith to the evaporator, where it passes intothe incoming solution. Here this heat causes some of said solution toevaporate, and the resultant vapor joins that already within theevaporator conduit. A counterflow heat exchange system 56 isdiagrammatically shown in FIG. l as a means by which the vapor leavingthe evaporator 18 may be superheated in zone 58 and this superheatsubsequently removed in zone 60.

The alternate embodiment illustrated in FIG. 2 encompass the generalaspects of this invention as described in FIG. 1 with like numeralsbeing -given to the same or functionally related parts. In thisparticular instance, however, the vapor ow direction is opposite to thatshown in FIG. 1 and the evaporator in this instance is a cylindricaltype, although it is to be understood that a diverging nozzle effect mayalso be embodied in this design similar to that shown in FIG. 1. Allother aspects of that other embodiment remain the same.

Alternative embodiments illustrated in FIGS. 3 and 4 encompass thegeneral aspects of this invention as described in FIG. 1 with likenumerals being given to the same or functionally related parts, withexceptions to be described. Basic to all embodiments is the surroundingannular heat exchanger. The embodiments of FIGS. 3 and 4, however,replace the recirculating vapor evaporator and condenser arrangement ofFIGS. 1 and 2, but may retain the superheat arrangement of these latterfigures.

In FIG. 3, raw liquid at substantially boiling temperature is fed intothe evaporator 18, which is centrally located in the apparatus and issurrounded by the condenser A20. This evaporator has heat conductingwalls of surface area suicient to the desired heat transfer and isconnected to a compressor 21 which operates either in steady orintermittent llow.

This compressor causes a pressure increase of the vapor flowing into thecondenser 20 so that the temperature in the latter is increasedsufficiently to allow the desired rate of heat transfer from thecondenser through the walls of and into the evaporator 18. Thus, heat ofcondensation is removed from the vapor in condenser 20 and issimultaneously added to the liquid in evaporator 18, where it suppliesthe heat of evaporation to a quantity of liquid equivalent to thequantity of vapor condensing.

An intent of this process is that the temperature and pressuredifferential be held low enough that the heat transfer occurs nearlyisothermally.

A certain proportion of the liquid in the evaporator must be removed,again in counterow heat transfer, with the incoming raw liquid, in orderto prevent an excessive accumulation of solute in the evaporator.

Heat losses may be made up by having a heat source, such as a heatingcoil 70, which is connected to an external source, and located in theevaporator. A system of check and oat valves will prevent reverse iiowand maintain the proper Aliquid levels in evaporator 18 and condenser20.

In FIG. 4 raw liquid at substantially boiling temperature is fed intothe evaporator 18 which is centrally 1ocated in the apparatus and issurrounded by the condenser 20. This evaporator has insulated wallsthrough which at least one heat pump with its circulating systempenetrates. The heat pump shown by the reference letter P in FIG. 4,with its system removes heat from the vapor in the condenser 20 throughthat portion 36 of its conduit which is in heat exchange with the vaporin condenser 20. The recirculating medium bearing this heat is thenraised in temperature, by means of externally supplied energy as at 71,suicient to cause flow of this heat to the raw liquid in the evaporator.Heat then flows from that portion 40 of the heat exchange conduit whichis in heat exchange with the raw liquid in evaporator 18. Again,exchanger surface areas are to be everywhere suiciently large to keeptemperature differentials between heated and heating media to the lowestpractical amount, consistent with desired rate of heat transfer, so thatthe heat transfer between the condenser and the evaporator approachesisothermal. As the raw liquid evaporates, it leaves the evaporator,which communicates by means of an opening with the condenser, and vaporows into the surrounding evaporator. In this case, the evaporator andthe condenser are at the same pressure.

Again, a certain proportion of the liquid in the evaporator must beremoved as concentrate and its heat yielded to the inilowing raw liquid.Heat losses are made up as needed by supplying external heat as at 70,and a system of check and float valves are provided to prevent reverseflow and maintain proper liquid levels.

Theoretically this invention approaches the effect and purposes of usingcounterflow heat transfer to bring a raw solution to its boilingtemperature and to recover this heat from the leaving liquids. Further,the heat of evaporation is supplied by recovering the heat ofcondensation from a given weight of vapor, raising the temperature ofthe medium bearing this heat by the alternative means discussed, andreturning this heat to the raw solution,

which has previously been raised to near boiling temperature. If any andall heat losses are made up from external sources, the heat ofevaporation is supplied to essentially an equal weight of raw solution,which converts the latter to steam. Essential to the operation of thisinvention is the maintenance of desired temperature difierentials at allheat transfer locations.

Entropy losses are minimized by everywhere transferring heat betweenmedia which are close in temperature to one another. Other energy lossesare substantially eliminated by recovering the pump work and byproviding that the leaving liquids be at substantially the temperatureof the entering liquid.

Aslo essential is that the temperature of the outside wall of theapparatus be very close to ambient. This is provided for by insulationand by having the outermost passageway of the heat exchanger wall 12 befilled with raw liquid at substantially ambient temperature.

Wherever this method has been described with respect to de-salting seawater, it is should be understood that the method is neverthelessapplicable to any distillation process involving any liquids and thatsuch are to be considered within the scope of the appended claims.

As used herein and in the claims, the following terms are defined: U

Raw Liquid: that undistilled liquid whose solute is to be removed.

Concentrate: that liquid removed undistilled from the evaporator whoseconcentration of solute is significantly higher than that of the rawliquid.

Condensate: that pure distilled liquid which results from condensationof the vapors generated by evaporating the raw liquid.

1. Apparatus for purifying a liquid by distillation comprising, incombination: an interconnected evaporator and condenser having wallswhich constitute the boundary of a cyclic path everywhere designed forminimum ow drag, said path having an enlarged portion whose ilow areahas relatively large cross-section and also having a constricted portionwhose ow area has relatively small cross-section, a stagnation chamber,said walls having at least one vaporexit aperture opening into saidstagnation chamber which thus forms a receptacle connected to saidcyclic path and so oriented as to receive a portion of the vapor flow,said chamber being in indirect contact with said constricted portion ofthe cyclic path by virtue of said chamber and said constricted portionbeing separated by the walls of said constricted portion, said wallsbeing constructed of heat conducting material at the places where saidwalls are a boundary between said stagnation chamber and saidconstricted portion of the cyclic path, said vapor-exit aperture beingat a portion of said path which is' neither at its enlarged portion norat its constricted portion, but at a portion intermediate to these,whereby in operation a portion of the vapor owing from said enlargedportion is diverted through said vapor-exit aperture into saidstagnation chamber, there to condense, said walls having at least oneliquid-entrance aperture immediately upstream of said enlarged portionwith regard to vapor flow for introducing liquid to be evaporated intosaid path in countercurrent lm ow, means to remove concentrated liquid,and means for imparting directed ow to said vapor along said path bymechanical movement of an impeller, whereby said vapor is maintained inaerodynamically effcient ow, said constricted portion increasing thevelocity and reducing the pressure and temperature of said vapor in saidconstricted portion to below that in said stagnation chamber so as tocondense the vapor in said stagnation chamber, means to removecondensate therefrom and heating means adapted initially to establishtemperature conditions within the system and continuously to provide theadditional heat necessary to replace any losses.

2. Apparatus according to claim 1 wherein said path comprises a closed,endless, cyclic vapor flow circuit whereby vapor is maintained inaerodynamieally eicient dow; wherein said constricted portion comprisesa nozzle or nozzles to provide converging ow, said nozzle or nozzleshaving heat-conductive walls; wherein said enlarged portion providesdiverging ow, whereby the temperature in the vicinity of said enlargedportion increases and said liquid in the vicinity of said enlargedportion vaporizes, which vapors join said recirculating vapor; andwherein said condensation region includes said stagnation chamber whichsurrounds said nozzles or nozzles so that said portion of thecirculating vapor which has been diverted into said chamber is cooled byheat conduction therefrom through said nozzle walls and condenses.

3. Apparatus for purifying a liquid by distillation coinprising incombination a first enclosure, a second, thermally insulated enclosurewithin said rst enclosure, means to introduce liquid to be evaporatedinto said thermally insulated enclosure, means for maintaining theinterior of both enclosures near the boiling point of said liquid, andheat pump type means for conveying heat into said thermally insulatedenclosure from said rst enclosure so that evaporation takes placetherewithin while condensation occurs outside said thermally insulatedenclosure and within said first enclosure and heating means adaptedinitially to establish operative temperature con-- ditions within thesystem and continuously to provide the additional heat necessary toreplace any losses.

4. Apparatus for purifying a liquid by distillation in which the liquidto be purified is preheated in heat exchange with the products ofcondensation and evaporation, namely condensate and concentrate,comprising in combination: a peripheral heat exchanger including acircumscribing inlet passageway for the distilland and contiguous outletpassageway for the condensate and concentrate respectively, said outletpassageways being in counterow heat exchange with said inlet passageway,an evaporator and a condenser adjacent thereto mounted within said heatexchanger so as to be thermally insulated by said heat exchanger fromthe environment of the apparatus, means for introducing distilland fromsaid inlet passageway into said evaporator, means for introducingconcentrate from said evaporator into one of said outlet passages, meansfor transferring vapor formed in said evaporator to said condenser,means for condensing vapor in said condenser, means for introducingcondensate from said condenser into the other of said outlet passages,means for removing heat from said condenser and recovering said heat insaid evaporator and heating means -for initially establishing operativetemperature conditions within the system and continuously providing theadditional heat necessary to replace any losses.

5. Apparatus according to claim 4, wherein said means for recoveringheat in said evaporator comprises a thermally conductive enclosuresurrounding said evaporator and surrounded by and in contact with saidcondenser, and a compressor adapted to transfer vapor from within saidenclosure to the surrounding condenser.

6. Apparatus according to claim 4, `wherein said recovering heatcomprises a thermally insulated enclosure surrounding said evaporatorand surrounded by said condenser, and a heat pump including externalenergy source for transferring heat into said enclosure from thecondenser surrounding said enclosure.

7. Apparatus according to claim 4 wherein said peripheral heat exchangerpassageways comprise concentrically arrayed exchanger surfaces, wherebythe temperature varies on any radial such that said temperatureapproaches that of said evaporator as distance from said evaporatordecreases, and said temperature approaches that of said environment asdistance from exterior of said apparatus decreases.

8. Apparatus according to claim 7, wherein said means for recoveringheat comprises an endless passageway hav- 7 ing a constricted portionnear and thermally connected to said condenser and having an enlargedportion near and thermally, and directly connected to said evaporator,and means for impelling some of said vapor around said endless passage.5

References Cited UNITED STATES PATENTS 3,394,054 7/1968 Hoham 202-195 X10 2,389,789 11/1945 Latham Ir. 203-10 X 2,793,988 5/1957 Latham Jr.203-11 X 3,026,256 3/ 1962 Liljeblad et al 165-47 X 8 Kratz 21M-154.2Lens 159-'17 R Loebel 202-236 X Ravenhorst 165-66 Chambers 203-11Vandenberg 203-11 Turner 159-46 JACK SOFER, Primary Examiner U.S. C1.X.R.

